The probability of the dominant allele in the population. Remember that can appear in the homozygous dominant phenotypes(p2
) or the heterozygous (pq). So p2
+ 2pq is the probablity of the dominant phenotype in the population. Since q2
is the recessive phenotype probablity, take the square root of that frequency and you'll have q. Subtract this from 1 to find p.